In general, image sensors are semiconductor devices that convert an optical image to an electric signal. Image sensors are classified into charge-coupled devices (CCDs) and CMOS image sensors (CISs). A CCD is a device in which metal-oxide-silicon (MOS) capacitors are disposed very close to each other, and charge carriers are stored in and transferred through the MOS capacitors. In contrast, a CMOS image sensor is a device employing CMOS technology, which uses a control circuit and a signal processing circuit as peripheral circuits, such that a number of MOS transistors, each associated with a unit pixel, are formed on a semiconductor substrate, whereby outputs of the respective unit pixels are sequentially detected by the MOS transistors by a switching method.
In addition, thermal infrared-ray image sensors, which are another type of image sensors include a lens for concentrating thermal infrared-rays emitted from an object having a constant temperature, thermal infrared-ray sensing elements, and a readout chip for extracting signals obtained by the thermal infrared-ray sensing elements. The thermal infrared-ray sensing elements may be classified into a semiconductor-type thermal infrared-ray sensing element using semiconductors and a heat-type thermal infrared-ray sensing element using thermal effects.
The semiconductor-type thermal infrared-ray sensing element includes a material having a low band gap, and thus, when thermal infrared-rays are incident thereto, electrons and holes are excited by the thermal infrared-rays, whereby the semiconductor-type thermal infrared-ray sensing element has high sensitivity. In such a semiconductor type thermal infrared-ray sensing element, a readout chip for processing signals requires a high gain and complicated noise processing, and thus an infrared ray sensor including the semiconductor-type thermal infrared-ray sensing element is generally manufactured using a CMOS manufacturing process.
On the other hand, in the heat-type thermal infrared-ray sensing element, when thermal infrared rays focused on a lens are incident on a thermal infrared ray absorbing part, the thermal infrared ray absorbing part absorbs the thermal infrared rays, thereby increasing the temperature thereof to capture a thermal image. In the heat-type thermal infrared-ray sensing element, any one method selected from a method of using a phase transition material sensitive to temperature, a method of using characteristics of ferroelectrics according to temperature, and a method of using a thermal electromotive force when a temperature increases may be used.